Use of the FM Subcarrier for transmission of digital data has been developed and used for more than a decade in Europe. The FM Subcarrier data transmission system developed in Europe is known as the Radio Data System (RDS) standard. The Radio Data System (RDS) standard has been adopted and extended for use in North America through the National Association of Broadcasters. The North American version is known as the Radio Broadcast Data System (RBDS). The Radio Broadcast Data System (RBDS) system of FM Subcarrier data transmission has been used for several years in North America.
The RDS/RBDS standards allow for a variety of simple data transmission applications such as broadcast of station identification, time synchronization, and information about the current artist or song that is being played. RDS has also been used for the transmission of differential GPS data and for the transmission of paging information. Radios that support the RDS/RBDS standards allow listeners to:                See the call letters of the tuned radio station.        Tune a radio station by selecting a radio program format (e.g. top 40, sports, oldies, jazz, country, talk radio etc.).        View song titles and artist names.        Hear traffic bulletins automatically.        Respond to emergency alerts. For example, radios turn on and interrupt in-car CD players and cassette players for traffic or emergency alerts.        Check paging messages.        View short information messages such as stock quotes, sports scores, restaurant/hotel directions, etc.        Synchronize clocks automatically.        Receive the phone number or contact information for RBDS advertisers.        
In December 1994, the United States Federal Communication Commission (FCC) announced its support for using RBDS technology to transmit Emergency Alert System (EAS) alerts in times of local or national emergencies over FM broadcast stations. The FCC recommendation is not only clear evidence that RBDS technology is viable today, but clear direction that broadcasters should consider RBDS an integral part of our nation's radio broadcasting infrastructure for the foreseeable future. As of August 1998, there were 300 radio stations broadcasting digital data using the RBDS standard.
The RBDS/RDS signals are low bit rate data streams transmitted on the 57 kHz subcarrier of an FM radio signal. The RBDS/RDS data rate is 1,187.5 bits per second. However, ten out of every twenty-six bits transmitted are used for error correction coding that is used to combat signal distortions that occur in the transmission path. Consequently, there is only about 730 bits per second of usable data bandwidth in an RDS signal. The data in the RDS signal is transmitted in 104-bit groups, each of which consists of four 26-bit blocks. Since ten of the twenty-six bits in each block are used for error correction coding, there are sixteen bits of information in each block. The type of information included in each block is dependent on the group type. There are 32 different group types (0A, 0B, 1A, 1B, . . . , 15A, and 15B). Certain types of information, such as the Program Identification (PI) code used to identify the transmitting station, are transmitted in every group type.
In essence, the RBDS/RDS and similar standards allow for the low bandwidth one way transmission of information from a broadcaster to suitably equipped radio receivers. The RBDS/RDS standards do not deal with interactivity in any way nor do they provide any capability for the receiver or audience of receivers to provide feedback to the broadcaster. There is also no way for the RBDS/RDS or other such systems to acquire additional information from other media which is or which can be coordinated with the audio broadcast. Although the RBDS/RDS systems provide useful features, it would be desirable for these services to provide a more interactive system. Furthermore, it would be desirable to increase the bandwidth such that additional information can be sent to the listener.